1. Field of the Invention
The present invention relates to a timepiece movement and, more particularly, to a timepiece movement having independently rotatable minute and hour wheels and which can detect a respective reference position of the minute wheel and the hour wheel.
2. Background Information
An example of a conventional timepiece movement of the kind to which this invention relates is described in Japanese Published Patent Application No. Shou 61(1986)-118683. Such a conventional timepiece movement detects when an hour hand, minute hand and second hand are displaying the time 12 o'clock (i.e., 12 hours, zero minute and zero second), detects any difference (error) between the time of which this 12 o'clock time is displayed and the time at which a radio time signal or similar broadcast time signal for that hour is received, and, every 12 hours, corrects any error in the time displayed by the timepiece.
In one example disclosed in Japanese Published Patent Application No. Shou 61(1986)-118683, when respective openings in an intermediate wheel, an hour wheel and a minute wheel become aligned once per revolution of the hour wheel, i.e., once every 12 hours, light from a first luminous or light-emitting device mounted on a circuit board passes through the openings and is detected by a first light-receiving device mounted remote from the circuit board. The first light-receiving device then outputs a reference position signal denoting that the hour wheel and the minute wheel are in their reference positions. Similarly, once per revolution of the second hand, i.e., once per minute, when openings in an intermediate wheel and a second wheel become aligned, light from a second light-emitting device mounted on the circuit board passes through the openings and is detected by a second light-receiving device mounted remote from the circuit board, and the second light-receiving device then outputs a reference position signal denoting that the second wheel is in its reference position. When the two reference position signals are being outputted at the same time, it is judged that the time 12 o'clock is being displayed.
In a second example disclosed in Japanese Published Patent Application No. Shou 61(1986)-118683, in order to enable both the light-emitting devices and the light-receiving devices to be mounted on the circuit board, the first and second light-receiving devices are disposed in the same positions on the circuit board as the first and second light-emitting devices are disposed in the above first example, and a single light-emitting device is also mounted on the circuit board. Two light-conducting bodies are used to guide light from the light-emitting device to the positions where the first and second light-receiving devices are disposed in the above first example.
However, with the first example referred to above, there is the problem that because the two light-receiving devices which face the two light-emitting devices are disposed remote from the circuit board, wires have to be provided to electrically connect both of the light-receiving devices to circuitry on the circuit board. The installation of these wires is an awkward and time-consuming task, whereby the timepiece movement cannot be easily mass-produced. In addition, misalignment between the light-emitting devices can occur during assembly or during use, which makes it impossible for the reference positions to be precisely detected.
In the case of the second example referred to above, there is the problem that, in order to mount the single light-emitting device and the two light-receiving devices on the same circuit board, two light-conducting bodies have to be installed. The light-conducting bodies have to be disposed in a confined space, whereby the construction of the timepiece movement is made complicated and the cost of manufacture is increased.
Another conventional timepiece movement of the kind to which this invention relates is described in Japanese Published Patent Application No. Hei 6(1994)-148354 which discloses an apparatus in which a detecting means is provided in each of the driving systems which respectively drive an hour hand and a minute hand. The detecting means comprises; a light sensor having a luminous element, a light-receiving element, and an opening provided in a gear train of each of the driving systems. The detecting means can detect when the hour wheel and the minute wheel are in predetermined reference positions, such as the 12 o'clock position.
However, in the conventional timepiece movement disclosed in Japanese Published Patent Application No. HEI6(1994)-148354, since the detecting means provided in each of the driving systems which respectively drive the hour hand and the minute hand comprises a light sensor (e.g., reflecting photosensor), separate wires have to be provided to electrically connect these detecting means to the circuitry of the timepiece. The installation of these wires is an awkward and time-consuming task which render the structure of the timepiece and assembly thereof complex. Furthermore, the high cost of reflecting photosensors increases the overall manufacturing cost of the timepiece movement.